The point of using Inkscape is to give you a Vector image. As soon as you export it and import it into MSWord it becomes rasterised and wastes the work you've done in Inkscape.
The reason why vector images are better is that they are stored as mathematical formulae that the computer can use to recreate the image at any size. The raster images are stored as instructions to recreate the original image size (something along the lines of 3 pixels blue, 2 pixels green, 1 pixel red, 5 pixels off...etc) Hence the great difference in the size of the saved file.
I don't use Inkscape, I use Illustrator, but the methodology would be pretty much the same. Work on an artboard (or whatever Inkscape calls the page) at a size proportional to your final image, in fact of the size of your final requirements is best.
The reason why vector images are better is that they are stored as mathematical formulae that the computer can use to recreate the image at any size. The raster images are stored as instructions to recreate the original image size (something along the lines of 3 pixels blue, 2 pixels green, 1 pixel red, 5 pixels off...etc) Hence the great difference in the size of the saved file.
I don't use Inkscape, I use Illustrator, but the methodology would be pretty much the same. Work on an artboard (or whatever Inkscape calls the page) at a size proportional to your final image, in fact of the size of your final requirements is best.